Zoster Immune Globulin (ZIG) is the first effective therapeutic agent for the prevention and attenuation of varicella. Our program, unique in its production of sufficient ZIG to meet all regional demands in the past year, has moved steadily to define the dosage, timing, and indications for ZIG in high-risk patients for prevention, attenuation and possible treatment of chickenpox. We are also gathering data to permit assessment of ambulatory and institutional needs. Our present research in Zig has amply confirmed its remarkably uniform action, its high potency and, therefore, small volume of inoculum, its reliability when administered on the basis of body weight, its freedom from adverse effects. We believe that due to these favorable properties and to the sharply rising demand for ZIG from our V-Z program and from the CDC's regional consultant group, we are on the verge of expansion into a long- range national program, acutely needed for three situations: 1. The sharply increasing number of children undergoing renal and other organ transplantations, or who are suffering from leukemia, Wilm's tumor, and other neoplastic diseases, who are becoming more susceptible to lethal complications of varicella due to the extension of their life by immunosuppressive drugs, corticosteroids, and radiotherapy. 2. Varicella pneumonia, at times fatal, a hazard to any otherwise healthy nonimmune adult. 3. Each institutional exposure poses special threats to the usual modern-day concentration of high-risk children as well as a difficult and costly administrative problem for a period of three weeks or more. Our methodology consists of continuous physician and paraprofessional education, donor recruitment with rapid identification and plasmapheresis, and careful clinical testing of each lot in the three areas of need outlined above. Effectiveness is measured in terms of controlled clinical study, short-term and long-term serological testing for immune response, and examination for specific complications. After the second three-year period we shall have refined our knowledge of ZIG to meet most clinical inquiries.